1. Field of the Invention
The present invention relates to a forklift structured such that baggage carried on a fork can be pushed out by a pusher movable forward in synchronization with the backward movement of a vehicle body.
2. Description of the Related Art
Conventionally, as a forklift of this type, there is known a forklift as shown in FIG. 6. The forklift comprises an electric vehicle body 1 which includes a mast 2 in the front portion thereof and an elevator body 3 so disposed on the mast 2 as to be movable upward and downward; and, there is provided a fork 4 on the elevator body 3 in such a manner as to project forwardly from the elevator body 3. And, a pusher 6 is mounted on the elevator body 3 through a pantograph-like link mechanism 5 and, between the elevator body 3 and link mechanism 5, there is interposed a pusher cylinder 7 which expands and compresses the link mechanism 5 to thereby move the pusher 6 forward, that is, in the direction of an arrow line xe2x80x9caxe2x80x9d as shown in FIG. 6 (forward movement xe2x80x9caxe2x80x9d) and backward, that is, in the direction of an arrow xe2x80x9cbxe2x80x9d shown in FIG. 6 (backward movement xe2x80x9cbxe2x80x9d) along the upper surface of the fork 4. Also, on the elevator body 3, there is disposed a pusher moving amount detector 9 composed of a potentiometer or the like which can detect the moving amount of the pusher 6 from the pull-out length of a cable body 8 connected to the pusher 6. Further, a vehicle speed detector 1c is disposed on a vehicle drive motor 1b which is mounted within the vehicle body 1. Also, as shown in FIG. 7, in the controls 1a of the vehicle body 1, there are disposed a steering wheel 10, a throttle pedal 11, a pusher lever 12, a synchronous mode change-over switch 13, a synchronous mode lamp 13a, and a forward/backward moving lever 14.
Conventionally, as shown in FIG. 8, in an oil pressure circuit 16 which connects together the pusher cylinder 7 and an oil pressure pump 15, there is disposed a proportional electromagnetic control valve 17 having four ports and three positions. Reference character 18 designates a drive motor for driving the oil pressure pump 15, while 19 stands for an oil pressure tank.
In the above-mentioned structure, as shown by a solid line in FIG. 6, while baggage W is carried on the fork 4, if the synchronous mode change-over switch 13 is depressed, the forward/backward moving lever 14 is switched from the neutral position thereof to the backward moving side thereof, and the throttle pedal 11 held at the neutral position thereof is stepped down, then a synchronous mode is operated; and, at the same time when the vehicle body drive motor 1b is driven and the vehicle body 1 is thereby moved backward xe2x80x9cbxe2x80x9d, the pressure oil supply amount is adjusted by the proportional electromagnetic control valve 17 which has been switched over to a right side expansion position A according to the amount of step-down of the throttle pedal 11 to thereby control the expansion speed of a piston rod 7a, whereby the pusher 6 is moved forward a in synchronization with the backward movement b of the vehicle body 1 to thereby push out the baggage W on the fork 4 (see an imaginary line shown in FIG. 6).
Thereafter, the synchronous mode can be removed by depressing the synchronous mode change-over switch 13.
However, in the above-mentioned conventional forklift, in order to move forward the pusher 6 in the arrow line a direction in synchronization with the backward movement xe2x80x9cbxe2x80x9d of the vehicle body 1, there is used an expensive proportional electromagnetic control valve 17, which leads to the expensive manufacturing cost of the forklift.
In view of the above, there can be expected a structure in which, instead of the expensive proportional electromagnetic control valve 17, there is used an inexpensive hand-operated switch valve and the hand-operated switch valve is operated by hand using the pusher lever 12. However, in this structure, if an operator operates the hand-operated switch valve in a smaller amount than a set operation amount to thereby control or reduce the pressure oil supply amount to the pusher cylinder 7 too much, then the synchronous operation may be performed incorrectly, thereby causing the properly arranged pieces of baggage to collapse or become rearrangred in a state of disorder.
Further, in the above-mentioned conventional forklift, since the synchronous mode change-over switch 13 is distant from the steering wheel 10 and pusher lever 12, each time the synchronous mode is switched, an operator must release his or her hand from the steering wheel 10 or pusher lever 12 and press down the synchronous mode change-over switch 13, which results in a poor operation efficiency. Also, to remove the synchronous mode after completion of the operation in the synchronous mode, it is necessary to press down the synchronous mode change-over switch 13, which takes time and labor.
Furthermore, in the above-mentioned conventional forklift, the moving amount of the pusher 6 is detected by the pusher moving amount detector 9, the speed of the vehicle body 1 is detected by the vehicle speed detector 1c from the number of rotations of the axle shaft or motor shaft, and, in accordance with the detect signals respectively issued from the two detectors 9 and 1c, the backward movement xe2x80x9cbxe2x80x9d of the vehicle body 1 and the forward movement xe2x80x9caxe2x80x9d of the pusher 6 are allowed to synchronize with each other. However, when the tire 1d is worn due to use for a long period of time, there is produced an error between the actual vehicle speed and the detected vehicle speed.
Also, in the conventional structure, because no means is disposed for correcting the above-mentioned error, the forward movement xe2x80x9caxe2x80x9d of the pusher 6 can be faster than the backward movement xe2x80x9cbxe2x80x9d of the vehicle body 1, which not only makes it impossible to place the pieces of baggage W at their respective given positions but also may lead to the pieces of baggage W collapsing or becoming rearranged in a state of disorder.
The object of the present invention is to eliminate the drawbacks found in the above-mentioned conventional forklift and to provide a forklift which can be manufactured at a low cost and is able to carry out a synchronous operation positively to thereby unload the baggage safely therefrom.
It is another object of the invention to provide a forklift which not only allows an operator to press down a synchronous mode change-over switch without releasing his or her hand from a pusher lever, but also allows the synchronous mode to be removed automatically after completion of the operation in the synchronous mode.
It is also an object of the invention to provide a forklift which allows the backward movement of the vehicle body of the forklift and the forward movement of the pusher to synchronize with each other with no error between them.
In attaining the above object, according to a first aspect of the invention, there is provided a forklift structured such that, while baggage is carried on a fork, if a synchronous mode change-over switch is depressed, a forward/backward moving lever is switched over to its backward moving side, and a throttle pedal is stepped down, then a pusher is moved forward by a pusher cylinder in synchronization with the backward movement of the vehicle body of the forklift to thereby push out the baggage on the fork, wherein, in an oil pressure circuit for connecting together the pusher cylinder and an oil pressure pump, there is disposed a hand-operated switch valve, and there is disposed a valve full-open switch for detecting that the hand-operated switch valve is fully opened, and also wherein, on receiving a detect signal form the valve full-open switch, a synchronous mode is operated.
According to the above structure, there is disposed the inexpensive hand-operated change-over valve in the oil pressure circuit connecting together the oil pressure pump and the pusher cylinder which is used to move the pusher forward in synchronization with the backward movement of the vehicle body, which makes it possible to reduce the manufacturing cost of the forklift. Also, since the synchronous mode is operated on receiving the detect signal sent from the valve full-open switch which can detect that the hand-operated switch valve is opened fully, there is prevented the possibility that, as in the conventional forklift, the pressure oil supply amount to the pusher cylinder can be excessively reduced to thereby cause a poor synchronous operation. Thanks to this, the synchronous operation can be carried out positively and thus the baggage on the fork can be unloaded safely.
According to a second aspect of the invention, the valve fall-open switch comprises a micro switch which is so disposed as to be opposed to the projection portion provided on and projected from the pusher lever for switching the state of the hand-operated switch valve. In operation, if the pusher lever is moved toward its forward moving side to thereby open the hand-operated switch valve fully, then the projection portion is contacted with the micro switch to thereby allow the micro switch to output a detect signal.
According to the present structure, it is possible to confirm that the hand-operated switch valve is opened fully using a simple structure which is composed of the projection portion provided on and projected from the pusher lever and the micro switch so disposed as to be opposed to the present projection portion, which allows the forklift to be manufactured at a low cost.
According to a third aspect of the invention, there is provided a forklift structured such that, while baggage is carried on a fork, if a synchronous mode change-over switch is depressed, a forward/backward moving lever is switched over to its backward moving side, and a throttle pedal is stepped down, then a pusher is moved forward by a pusher cylinder in synchronization with the backward movement of the vehicle body of the forklift to thereby push out the baggage on the fork, wherein the synchronous mode change-over switch is mounted on a pusher lever used to operate the pusher cylinder.
According to the above structure, since the synchonous mode change-over switch is mounted on the pusher lever, an operator is able to press down the synchronous mode change-over switch to thereby switch the synchronous mode without releasing his or her hand from the pusher lever.
Also, according to a fourth aspect of the invention, there is provided a forklift structured such that, while baggage is carried on a fork, if a synchronous mode change-over switch is depressed, a forward/backward moving lever is switched over to its backward moving side, and a throttle pedal is stepped down, then a synchronous mode is operated by a control part comprising a microcomputer and a pusher is moved forward by a pusher cylinder in synchronization with the backward movement of the vehicle body of the forklift to thereby push out the baggage on the fork, wherein the control part is structured such that it is able to remove the synchronous mode in accordance with not only the detect signal notifying that the pusher lever for operating the pusher cylinder and throttle pedal have been returned to their respective neutral positions but also the detect signal notifying that the pusher has moved most forward.
According to the above structure, after completion of the operation in the synchronous mode, the synchronous mode can be automatically removed by the control part in accordance with not only the detect signal notifying that the pusher lever and throttle pedal have been returned to their respective neutral positions but also the detect signal notifying that the pusher has moved most forward. This eliminates the need that, as in the conventional forklift, the synchronous mode is removed by pressing down the synchronous mode change-over switch. Therefore, the present invention does not take time and labor but can provide a high operation efficiency.
According to a fifth aspect of the invention, there is provided a forklift structured such that, while baggage is carried on a fork, if a synchronous mode change-over switch is depressed, a forward/backward moving lever is switched over to its backward moving side, and a throttle pedal is stepped down, then a pusher is moved forward by a pusher cylinder in synchronization with the backward movement of the vehicle body of the forklift to thereby push out the baggage on the fork therefrom, wherein there is disposed an output adjusting device which is used to adjust the output of an oil pressure pumpdrive motor for driving an oil pressure pump for the pusher cylinder or the output of a vehicle body drive motor.
According to the above structure, when there is produced an error between the actual vehicle speed and the detected vehicle speed, for example, because the tire of the forklift vehicle body is worn due to use for a long period of time, the thus produced error can be corrected by adjusting the output of the oil pressure pump drive motor or vehicle body drive motor due to the operation of the output adjusting device, thereby allowing the backward movement of the vehicle body and the forward movement of the pusher to synchronize with each other with no error between them. Thanks to this, the pieces of baggage respectively pushed out from the fork by the pusher can be placed positively at their given positions without turning them into a state of disorder.
Also, according to a sixth aspect of the invention, in the invention of the fifth aspect of the invention, the output adjusting device comprises a variable resistor and, in accordance with an output signal issued from the present variable resistor, the output of the oil pressure pump drive motor or vehicle body drive motor is controlled by the control part comprising a microcomputer.
According to the above structure, because an inexpensive variable resistor is used, the manufacturing cost of the forklift can be reduced when compared with the conventional forklift. Also, in accordance with the output signal of the present variable resistor, the output of the oil pressure pump drive motor or vehicle body drive motor can be controlled accurately by the control part which comprises a microcomputer.